As a high-performance optical material, fused
silica is widely applied in high-power
laser and photoelectric systems. However,
laser induced damage (LID) of fused
silica severely limits the output power and performance of these systems. Due to the values in strong field physics and improving the load capacity and performance of high power systems at UV
laser, LID at 355 nm of fused
silica has attracted much attention. It has been found that, even be treated by advanced processing technologies, the actual damage threshold of fused
silica at 355 nm is far below the intrinsic threshold. It means that there is an absorption source near 355 nm in fused
silica. However, to date, the absorption source is still unknown. In this paper, a absorption source near 355 nm is found by first-principles calculations. We find that the absorption source near 355 nm is neutral
oxygen-vacancy defect (NOV, ≡Si-Si≡) and this defect originates from the
oxygen deficiency of fused
silica. Our results indicate that NOV defect can be taken as a damage precursor for 355 nm UV
laser, and this precursor can be obviously reduced by increasing the ratio of
oxygen to
silicon. Present work is valuable for exploring damage mechanisms and methods to improve the damage threshold of fused
silica at UV
laser.